The present invention relates to a coupling structure of shock transmitting member and a shock absorbing member, and to a bumper.
A shock absorbing member that includes a hollow shock transmitting member is known in the art. The shock transmitting member has a substantially constant cross section. When receiving an axial load, the transmitting member is plastically deformed and absorbs the impact energy. In such a shock absorbing member; a significantly great axial load needs to be applied to the absorbing member as shown in FIG. 4 to initiate plastic deformation (initial buckle deformation). Once a plastic deformation is started, the absorbing member consecutively repeats buckle deformations by relatively small axial loads with its shape turning into that of a bellows. In this manner, the absorbing member absorbs shock.
Such axial loads are transmitted to the outside through the shock absorbing member. Therefore, the great load at the initial stage is also transmitted to the outside through the absorbing member. Thus, the axial load that initiates plastic deformation (initial buckle deformation) of the shock absorbing member needs to be reduced. Accordingly, Japanese Unexamined Patent Publications Nos. 5-65076, 7-145842, 7-145843, 8-216917, 11-208518 disclose devices for reducing such load.
In the above publications, the shock absorbing members have a portion for concentrating stress, or a weakened portion. Plastic deformation due to axial load starts from the weakened portion, which reduces the axial load for initiating the plastic deformation. However, each of the shock absorbing members of the publications has more than one of the following drawbacks.
(1) Machining is complicated and difficult.
(2) Axial load for initiating plastic deformation is not sufficiently reduced.
(3) Due to design and structure, stable plastic deformation characteristics cannot be obtained.
(4) If holes are formed, consecutive buckle deformations create ruptures, which hinder reliable plastic deformations.
(5) Weld beads degrade the mechanical characteristics of a material. Therefore, when receiving a tension load, the shock absorbing member is likely to be broken.
(6) Attaching beads to a hollow body, the interior of which is divided into sections by walls, is complicated and difficult.
(7) Machining, such as cutting, increases the costs.
Accordingly, it is difficult to obtain stable and satisfactory characteristics and effective productivity at the same time.
Accordingly, it is an objective of the present invention to provide a coupling structure of a shock transmitting member and a shock absorbing member, and a bumper that improve the productivity and reduce axial load for initiating plastic deformation.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a coupling structure of shock transmitting member and shock absorbing member is provided. The coupling structure includes a shock transmitting member, to which load is applied, a hollow shock absorbing member, and a coupling structure. The hollow shock absorbing member has a substantially constant cross section, an open end, and an axis extending from the open end. The shock absorbing member is plastically deformed in the axial direction for absorbing load applied to the shock transmitting member. The coupling structure couples the shock transmitting member and the shock absorbing member. The shock transmitting member includes a projection, which faces part of the open end of the shock absorbing member.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.